Potato Res. 22 (1979) 29 39

The development of Rhizoctonia solani Kiihn on the underground parts of the potato plant

D O R O T H Y S P E N C E R and R .A. F O X

Scottish Horticultural Research Institute, Invergowrie, Dundee. Scotland

Accepted for publication: 3 October 1978

Zusamnlep~l~tssung, R~sum~; p. 37

Additional keywords." roots, stolons, tubers, hauhn destruction, harvest date

Summary

The development of the sclerotia (black scurf') of Rhizoctonia solani Kiihn, on potato tubers is related to tuber maturi ty and the health of the root and stolon systems, Few sclerotia formed on tubers from un- treated plants until the onset of plant senescence when, as the tubers matured and roots and stolons decayed, sclerotia developed both rapidly and extensively. Application of acid to haulms in early August led to an increase iq black scurf on tubers, initially related to the increase in root and stolon infection, but especially after later harvests, to the degree of tuber maturity. Later in August, scurf increases were parallel- ed both by tuber changes and root and stolon infection. My mid-September, when acid application was to plants becoming senescent, there was little difference between patterns of infection found on treated and check plants.

Introduction

All underground parts of the potato plant may be infected by Rhizoctonia solani Kiihn but the development of sclerotia on the tuber surface black scur f - is the commonest and most obvious symptom. These sclerotia are important in two ways: they transmit infection and thus influence seed production and certification, and, by disfiguring the tuber surface, they affect the sale of ware potatoes, especially those required for pre-packs.

Little is known of the physical, edaphic, and nutritional factors which may in- fluence the formation of the sclerotia. Hunt (1957) and Townsend (1957) both found that the nutritional requirements for the initiation of sclerotia of R. solani differed fromthose for their maturation. Similar differences must be expected to occur in the tubersphere to permit the formation of sclerotia. Nutritional changes derive from roots and stolons during their growth and decay but less obvious changes arise from the tuber directly as noted by Spencer & Fox (1978).

This paper describes the progress of infection by R. solani through a season on roots, stolons, and tubers and examines the influence of haulm destruction and the interval between it and harvest, on both infection and the development of sclerotia.

29

Materials and methods

DOROTHY SPENCER AND R. A. FOX

Seed tubers of the cv. Majestic, were selected as visibly free from black scurf and then inoculated at the rose end, just prior to planting by inserting four barley seeds each infested with a different isolate of R. solani originally obtained from sclerotia on potato tubers.

Treatments The experiment, sited at the Scottish Horticultural Research Institute. was laid out as a split plot design with four replicates, each plot consisting of ten plants. Haulms were either sprayed with acid or not on one of five dates and the plants harvested at intervals thereafter (Table I). From the tip, mid. and basal regions of roots and stolons 10-ram portions were removed. The samples were held in 75 m m • 25 mm tygan cylinders which were placed in running tap water for twenty minutes, rinsed in sterile water, dried on sterile paper towels and ten segments per sample then plated on 1.5",, tap water agar containing 50 mg each of neornycin and chloramphenicol per litre. The plates were incubated for 48 hours at room temperature (ca. 20 C) in diffuse light. Twelve seed tubers were removed from each plot and scored for the concentration of sclerotia (Table 2) and the severity of infection calculated as des- cribed by Spencer & Fox (1978). A rectangle of periderm tissue was removed on the long axis of each tuber starting at the rose end and the percentage removed was taken as an assessment of the maturity of the periderm, less being removed from older than younger tubers (Spencer & Fox, 1978).

mllr

The percentage of root segments infected by R. solani was very similar on samples from each of the three regions. The results were totalled and averaged to give the value for analysis of root infection as was also done with the data from stolons.

Table I. Dates of haulm treatment with acid spray (I)) alld harvest (H).

Haulm Dates of harvest; (H) treated

(H,,) H, H, H.~ H 4 H~ H,,

DI 5 Aug 12 Aug 19 Aug 26 Aug 2 Sep D2 14 Aug 21 Aug 28 Aug 4 Sep I I Sep D3 21 Aug 28Aug 4Sep I1Sep 18Sep 25Sep D4 2 Sep 9 Sep I6 Sep 23 Sep I Oct 8 Oct D5 12 Sep 16 Sep 26 Sep 3 Oct 10 Oct 17 Oct 24 Oct

I Kraut hehandelt Dc!/~ma,~,,c,; 2Erlltc'~ktlell Date.s ch" r&'ollc

Tabelle 1. Daten der Krautbehandlung durch Sfiurespritzung (D) und der Ernte (H). Tableau 1. Dates de dcfanage chimique (D) et de r6colte (H).

30 Potato Res. 22(1979)

UNDERGROUND SPREAD OF RHtZOCTONIA SOLANI

Table 2. Scor ing levels used to de te rmine the densi ty of selerot ia on the tuber surface.

Exposed area covered by sc le ro t ia ' (",,1

0 nil 2

I < 3 "~ > 3 20 3 > 20 60 4 > 60

~.4usgeset-te l-'leh'hc, die mit Skh,rotien hedeckt war .S'uUm'e couvertc par des sob;rotes." z Nul l Z~;ro

Tabel le 2. Bewer tungsgrade , die zur Bes t immung der Sk le ro t iend ich te au f der Knol lenoberf l f iche ver- wendet wurden. Tab leau 2. Echelle de no t a t i on utilisbe pour de te rmine r la densitd de sclerotes it la surl:ace du t u b e r c u l e

Data from root and stolon tissue were transformed before analysis. For ease of inter- pretation the original data are presented in Fig. 1 and 2. Significance levels are for P < 0.05. Duncan 's Multiple Range Test was applied to the data when necessary (Duncan, 1955).

Results

Roots and stolons on unsprayed plants were generally healthy until early September. Lesions of R. solani were frequent but both small and limited (Fig. 1 and 2) and the number of tissues infected did not significantly alter with time. As plants became senescent, roots and stolons decayed and there was a concomitant rise in infection.

The first three haulm treatments, D1, D2, D3, resulted in an increase in both stolon and root infection compared to check plants. With root tissues the increase was noted within a week of treatment but was significant only following D2 and D3. Stolon tissues were slower to react. There was a significant increase in infection be- tween H 2 and H 3 following D1 and also between H l and H_, following D2. By early September differences between check and treated plants were few and only one was significant - root tissues at H t. By mid-September, roots and stolons on check plants had become extensively infected by R. solani and saprophytes were colonising decayed tissue. Following the application of acid at D5, there was no significant difference in the amount of either root or stolon infection between treated and check plants.

The number of tubers from check plants bearing black scurf(Fig. 3) and the extent of this infection (Fig. 4) varied little with time until mid-September but between then and late September both properties doubled, these increases being significant. Killing hauhns with acid spray markedly increased the number of infected tubers and the extent of infection. The increases occurred in both values from one to three weeks after treatment and were significant between H t and H_, following D 1. D2, and D5, also between H 2 and H s following both D3 and D4.

Potato Res'. 22 (1979) 31

D O R O T H Y S P E N C E R A N D R. A, FOX

Fig. 1. Percentage of roots infected after two haulm treatments applied o13 five dates. D, Ds : Dates of haulm treatment - Daten de" Krat thehat d/un~ Dute th' dt!/ima.,.,,e. H,, H o: Times of harvest Erntezeiteu Dute~h'r(;cohe.

Infected (%) 100

0

H o

100

5O

0

100

5O

0

100

5O

0

IO0

5O

0 I I

~ FINo acid M ~ ~Acid spray

H I H 2 H 3 H 4

'H 0 H 1 H 2 H 3 H 4

~0 H H 2 H 3 H 4 H 5

D1 D2 D3 q)4 August

Infected h!l~ziert UoutanlinJ

H 0 H 1 H 2 H 3 H 4 H 5 M mMM t H H 1 H 2 [ H3 H 4 H 5 H 6

4 D5 I September October

No acid Olme S~'itu'e - Non ~h!/~Ul(; Acid spray - .5"(7 trespritzu/tg D(!/~uu; chiutiqueme/It

Ahh. I. P/'ozentsat: an in/~zierte/I H'urzeht m/tit : ,'ei K 'uuthel a/ulluu~e/1 ank, ewemh't un /i'i/l/ Dalen. Fig. 1. Pource/lta.~e (k" rttciues ('outamin(;es upr~;s d(,tt.v ch;/a/laXes appliqu(;s ~'1 ('i/tq dates d(/]~;reut(,.s.

32 Potuto Res. 22 (1979)

L I N D E R G R O U N D S P R E A D O F R H I Z O C T O N I A S O L A N I

Fig. 2. Percentage of stolons infected after two haulm treatments applied on five dates. D, D s, H,, H6: See Fig. I S i e h e Ahl~. I l 'oir./~,eure 1.

I00

50

0

t

Infected (%)

500[ ~ ~ ~ _ Q Acid spray

LHoH 1 H 2 H 3 H 4

OOo 0

H 0 H 1 H 2 H 3 H 4 H 5 I00

0

D D 2 D 3 August

H 0 H 1 H 2 H 3 H 4 H 5

f

) 4 D 5 September October

Percentage infected. No acid. Acid spray: S iehe .4hl~. 1 I 'o i r . l igure l .

Ahh . 2. P r o z e n t s a t z an D!/i 'zierlen S /o /~ u' I ~ "h - w e i Kr m t l w h a n d l u n ~ c m unL, c, w e n d e l cul /i'bl/ Da len . Fig. 2. P~ rcenta.~c de s t d m s c ~ rut inr apr~;~" th, t tu tt~;/~tltage.~" appliqut;s ~ umq tittles digit;re'hies.

P o t a t o Res . 22~ 1979) 9_

DOROTHY SPENCER AND R. A. FOX

Fig. 3. Number of seed tubers infected with black scurf after two haulm treatments app l i ed on five da tes .

D 1 D s, H a H6 : See Fig. 1 Siehe ,4hl~. I I:oirfigure 1.

Number i n f e c t e d 12

D 1 8

4

0 H 0 H 1 H 2 H 3

12

D 2 8

4

0 H 0 H 1 H 2 H 3

12

D 5

12

8

4

0

H 4

H 4

1 2

8 i

D 3

H 0 H 1 H 2 H 3

D 4

M H 0 H 1 H 2 H 3

8

0 H 0 H I H 2 H 3 H 4 H 5 H 6

No acid

[7 Acid spray

H 4 H 5

i

H 4 H 5

N u m b e r infected ,4,:ahl ilz[i'ziert Nomhre de tul)ercule.vzfils c'ontamim;s N o acid . Acid s p r a y : Siehe Ahh. 1 I'oir./~gu "e 1

Ahh. 3. Anzahl p/hmzknolh.n, die nach :wei Krauthehamll rage1 an~,ewemh't an./t'#!/ Daten. vtm Pocken- krankheit h(/~dle, warci1.

Fig. 3. Nomhre ~h" lubercule.~'-/i/s porteurs de sc'lt;rote.~' apr~;s deux &!/anage.~" al~pliqm;s ~ cinq ~h~tc's d(/]i;rentes.

The percentage of periderm removed from check tubers was high until mid-Sep- tember (Fig. 5). A marked decrease then occurred in the amount that could be removed and within a week there was a corresponding increase in both the number of tubers bearing scurf and its intensity on them. Acid-treated plants behaved differently: changes in the amount of black scurf were not necessarily related to changes in periderm maturity. Following the two August kills, D1 and D2, scurf had increased

34 Potato Res. 22f l979)

UNDERGROUND SPREAD OF RHIZO('TONIA SOLANI

Fig. 4. Severity of black scurf on seed tubcrs after two haulm treatmcnts applied on five dates. D~ Ds, H. Ho: See Fig. I Siehe Ahh. I l,'r I.

Severity

I D1 rn 150 D3

150 [ ~ 120r

120

0 HO H1 H2 H3 H4 0 HO HI H 2 H 3 H, H 5

150

i00

50

N F] 150

H 0 H I H 2 H 3 H 4

D 4

H 0 H 1 H 2 H 3 H 4 H 5

I i00 D

5O

0 H 0 H 1 H 2 H 3 H 4 H 5 H 6

No acid

Acid spray

Severity S('hwere Sc;v(;rilc; No acid. Acid spray: Siehc' AhlL I I'oir./igttrc' 1 Ahh. 4. Schwere ch'r P,,ckenkrankhc'it aul P/lan--kmd/c,n nac'h -wc'i ](r~/ttlhufl(l/ld/lt/IgCll. (IIIgUWc'Hd<'I ~1/I /iil!/ Date . . Fig. 4. Sc;v~;ritc; cht rhizoc'tonc' sur tuherculc'sz/ils aprc;s ~h'u.v ch!/hmtgc's appliquc;s ~'t cinq ~km's di[/(;rentc's.

by He a l t h o u g h at t h o s e t imes the p e r i d e r m c o u l d still be easily r e m o v e d . F o l l o w i n g

the th ree S e p t e m b e r t r e a t m e n t s , h o w e v e r , d i f f i cu l ty in r e m o v i n g the p e r i d e r m was

paralleled by increases in scurf on the tubers .

Potato Res. 22(1979) 35

DOROTHY SPENCER AND R. A. FOX

Fig. 5. Percentage of periderm strip removed from a tuber after two haulm treatments applied on five dates. D ~ - D 5. Ho-H~: See Fig. 1 - Siehe Abb. 1 - l.'oir./].~,ure 1.

100

Periderm removed (%) I00

o 1 I00 i 0 HI H2 H3

5O

0

I00 I 5O

0 H o

50

0

i00

0

I

50

H 4

H 2 H 3 H 4

H 1 H 2 H 3 H 4 H 5

'H 0 .H 1 H 2 H 3

from ~0 H1

No acid

F] Acid spray

FL H 4 H 5

D1 D2 D3 )4 D5 August September October

Periderm removed En(/erntes Peri(~rm PdridermeenlevO No acid, Acid spray: Siehe Ahh. l - b2Jir/ igurel

[]q Fln

I I

Ahb. 5. Prozentsatz der yon einer Knolle en(/ernten Peridermstre(/~,n nach zwei Krautbehandhmgen. an.oe- wendet an./i'il!f Daten. Fig. 5. Poureentage deJ)'a~ments de p~;riderme ayant (;t~ enlev( 6 partir de tuberctdes aprOs deux d~!/hnaff~es appliquOs t'l cinq dates d([]('rentes.

36 Potato Res. 22(1979)

UNDERGROUND SPREAD OF RHIZOCTONIA SOLANI

Discussion

The underground parts of check plants remained relatively healthy until mid- September with only limited infection from R. solani. In the following three weeks the tubers matured and as the roots and stolons became moribund both tissues were extensively infected by R. so/ani presumably as a consequence of its high degree of competitive saprophytic ability (Garrett, 1970). Thus the food supply for the thallus was altered both in quality and in quantity by a decrease from tubers as they aged (Spencer & Fox, 1978) and an increase from the enlarged food base provided by decaying roots and stolons. Townsend (1957) and Hunt (1957) noted that in vitro sclerotia initials would form under a given set of conditions, but changes were required for their maturation. The alteration of the food supply in vivo was paralleled here by a maturation of sclerotia. Thus by mid-September when nutritional changes occurred, there was an increase in the number of tubers infected with scurf and in the severity of infection.

The affect of hauhn kill on scurf levels varied with its time of application. When the haulm is killed growth ceases and the tubers would by expected to mature rapidly and roots and stolons to decay. Hauhn kill in early- to mid-August led to increases in the numbers of tubers with black scurf and, especially, in the severity of infection. These increases progressed with increasing intervals after haulm kill and were associated with increasing colonisation of roots and stolons and especially at H 3

and H., after the first two haulm kills - with increased periderm maturity. The effects of changes of root and stolon infection and periderm maturity following haulm destruction, became less evident with time and by early September no clear pattern remained. By then natural root and stolon decay had started and some plants were becoming senescent: thus acid application in mid-September little altered the pattern already developing in the check plants.

Acknowledgments

The work reported here was supported by a grant from the Potato Marketing Board which is gratefully acknowledged.

Zusammenfassung

Die Entwickhmg yon Rhizoctonia solani Kiihn an den unterirtfischen Teilen der Kar- to['/elp/lanze

In diesem Artikel wird der Fortlauf der lnfektion dutch Rhizoctonia solani K0hn an Wurzeln. Sto- lonen und Knollen beschriebcn. Fcrncr wird der Einfluss der Krautvernichtung und des zeitlichen Abstandes zwischen ihr und der Ernte auf diese lnfektion untersucht.

Pflanzknollen der Sorte Majestic wurden am Kronenende direkt vor dem Auspflanzen mit vier lsolaten von R. sohmi (ausSklerotien von Kartoffel- knollen) inokuliert. All den attsgelesenen Knollen war keine Pockenkrankheit sichtbar. Das Kraut wurde an einem yon fiinf Daten gespritzt resp.

Potato Res. 22 (1979) 37

nichl gespritzt und die Pflanzen nachher in Inter- vallen geerntel (Tabellc 1 ). Wurzel- und Stolonen- teile wurden gewaschen, dann auf Lcit ungswassera- gar. das 50 mg Neomycin und ChloramphenicoI pro liter enthielt, gebracht und vor dcr Beurteihmg auf Rhizoctoniabefall wiihrend 48 Stunden be, Zimmertemperatur bcbrfitet. Die Pfianzknollen wurden gem~iss Tabclle 2 auf Sklerotienbefall beurteih. Zur Reifeschiitzung wurde jede Knollc der Lfingc nach geschnitten und der Prozentsatz des Periderms not,err, das mit einer Pinzettc entfernt werden konnte, wenn man am Kronenende begann.

Die Kontrollpflanzen ha,ten bis Mitte Septem- ber be, nur beschrfinkter Iokaler lnfektion dutch R. so!an, IAbb. 1 und 2) relativ gesunde Unter- grundsysteme. In den folgenden drei Wochen reiften die Knollenperiderme. Wurzeln und Sto- Ionen wurden weitgehend vom Pilz besiedeh.

R6sum6

Diss&Tl imt t ion s o u t e r r a i n e de R h i z o c l o n i a s o / a m

Cet article d,Scrit l't}volution de la contamination. par Rhi2ocloJtia s+dam Kfihn. des racines, stolons et tubercules de pommes de terre, et examine l'in- fluence du ddfanage et de I'intcrvalle ddPanage- recoltd sur une telle contamination.

Des tubercules de la varidtO Majestic n'dtant pas visuellement porteurs de scldrotes ont dt~ inocul/rs :21 la couronne, juste awmt la plantation, avec 4 souches de R..~olam + pro~.enant dc sclcrotes stir tubercules de potatoes de terre. Les tiges on, 6td ou n'ont pas &,5 d,Sfan~es fi 5 dates differentes et on a r~coltd ensuite les tubercules 'a interwdles rdguliers (tableau 1 ).

Les fl'agments de racines et de stolons ont dt~ lavds, placds sur une gelose it I'eau du rob,net. contenant 50 mg de ndomycin et de chloramphdni- col par litre, et mis fi incuber 48 heures it temp6ra- lure ambiante avant notation de l'infection par R. sohmi. La notation des scl,~rotes sur tubercules- fils a 6tO effectu,Se comme cela est indiqu~ dans le tableau 2. Comme estimation de la 'maturitd' chaque tubercule a ,}tO coup0 selon l'axe longitudi- nal et on a note le pourcentage de p,hiderme, en partant de la couronne qui a pu t~tre enlev.b avec des pinces.

DOROTHY SPENCER AND R. A. FOX

Folglich finderte sich die NfihrstolTversorgung des Pilzes. einc Situation. yon der ,nun weiss, dass sie die Entwicklung zur Skterotienbildung t',Srdert. Mitte September widerspiegelt sich die Anderung in der Ernfihrung in einem Ansteigen de, Anzahl von Knollen mit Pocken und in deren Ausdehnung auf den Knollen {Abb. 3 und 4).

Krautvcrnichtung mit Siiure Anfang August ffihrte zu einer Zunahme der Pockenkrankheit. was anFdnglich aufeine Zunahme der Wurzel- und Stoloneninfektion. spfiter aber auf den Grad der Knollenreife (Abb. 5) in Beziehung stand.: Spfiter. im August. wurden die Krankheitszunahmen mit Knollen{inderungen wie mit Wurzel- und Stolonen- infektion gleichlaufend. Die S'.iureanwendung Mit- re September geschah an alternden Pflanzen und iinderte das an Kontrollpflanzen beobachtete In- fektionsbild wenig.

Les plantes t,Smoins ont eu leurs systdmes sourer- ruins relativement sains jusqu'fi Ia mi-septembre avec des contaminations locales par R..~'ohmi. limitees (figures I & 21. Les trois semames st, ivan- tes. la matu,itd des tubercules a augment,5 et les racines et stolons ont dtd fortement contamin,Ss par le champignon. Lc support nutritionnel du cham- pignon a done 0re altdrtL cet 61&nent connu permet de stimuler la maturit~ des sct,Stotes en cours de formation. Vers la mi-septembre, des change- ments nutritionnels se son, sold~3s par une aug- mentation du hombre de tuberculets porteurs de scl~rotes et par l'extension de ces derniers (figures 3&4) .

ke ddfanage aux colorants nitr6s d,Sbut ao0t a entraind une augmentation des scle.rotes, qui s'&ait lnanil'estde initialement pat une augmentation de la contamination des racines et stolons, et plus tard au niveau du degrd de maturitt} du tubercule (figure 5}. Plt, s tardivement cn aofit, l 'augmenta- tion des scldrotes allail de paire avec le changement de tubercule ct avec la contamination des racines et stolons. Vers ht mi-septembre, le dcfanage sur des plantes proches de lu senescence a eu un h?ger ef(et sur Ia contamination des plantes t,Smoins.

38 Potato Res. 22 (1979)

UNDERGROUND SPREAD OF RHIZOCTONIA SOLANI

References

Duncan, D. B.. 1955. Multiple range and multiple F tests. Biometrics I1: I 42. Garret, S. D.. 1970. Pathogenic root-infecting fungi. Cambridge University Press, pp. 294. Hunt. P.. 1957. Physiology ofsclerot ium fl)rmation. Ph .D. Thesis. University of Bristol. Spencer, Dorothy & R. A. Fox. 1978. Tile distribution of sclerotia of Rhizoctoniu sohmi K/.ihn on the

surface of the potato tuber. Potulo Res. 21 :37 46. Townsend, B. B.. 1957. Nutrilicmal factors influencing the production of sclerotia by certain fungi..4rot.

Bot..n.s. 21:153 166.

Potato Res. 22 (1979) 39